// Copyright (c) 2012 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#include "ui/views/animation/scroll_animator.h"

#include <algorithm>
#include <cmath>

#include "base/logging.h"
#include "ui/gfx/animation/slide_animation.h"

namespace {
const float kDefaultAcceleration = -1500.0f; // in pixels per second^2

// Assumes that d0 == 0.0f
float GetPosition(float v0, float a, float t)
{
    float max_t = -v0 / a;
    if (t > max_t)
        t = max_t;
    return t * (v0 + 0.5f * a * t);
}

float GetDelta(float v0, float a, float t1, float t2)
{
    return GetPosition(v0, a, t2) - GetPosition(v0, a, t1);
}

} // namespace

namespace views {

ScrollAnimator::ScrollAnimator(ScrollDelegate* delegate)
    : delegate_(delegate)
    , velocity_x_(0.0f)
    , velocity_y_(0.0f)
    , last_t_(0.0f)
    , duration_(0.0f)
    , acceleration_(kDefaultAcceleration)
{
    DCHECK(delegate);
}

ScrollAnimator::~ScrollAnimator()
{
    Stop();
}

void ScrollAnimator::Start(float velocity_x, float velocity_y)
{
    if (acceleration_ >= 0.0f)
        acceleration_ = kDefaultAcceleration;
    float v = std::max(fabs(velocity_x), fabs(velocity_y));
    last_t_ = 0.0f;
    velocity_x_ = velocity_x;
    velocity_y_ = velocity_y;
    duration_ = -v / acceleration_; // in seconds
    animation_.reset(new gfx::SlideAnimation(this));
    animation_->SetSlideDuration(static_cast<int>(duration_ * 1000));
    animation_->Show();
}

void ScrollAnimator::Stop()
{
    velocity_x_ = velocity_y_ = last_t_ = duration_ = 0.0f;
    animation_.reset();
}

void ScrollAnimator::AnimationEnded(const gfx::Animation* animation)
{
    Stop();
}

void ScrollAnimator::AnimationProgressed(const gfx::Animation* animation)
{
    float t = static_cast<float>(animation->GetCurrentValue()) * duration_;
    float a_x = velocity_x_ > 0 ? acceleration_ : -acceleration_;
    float a_y = velocity_y_ > 0 ? acceleration_ : -acceleration_;
    float dx = GetDelta(velocity_x_, a_x, last_t_, t);
    float dy = GetDelta(velocity_y_, a_y, last_t_, t);
    last_t_ = t;
    delegate_->OnScroll(dx, dy);
}

void ScrollAnimator::AnimationCanceled(const gfx::Animation* animation)
{
    Stop();
}

} // namespace views
